Endoskeletti

Endoskeletti is the internal skeleton of an organism, forming the main support and framework from within the body. In most vertebrates, it comprises bone in living tissue and a variable amount of cartilage during development, with bone tissue replacing cartilage. In some invertebrates, such as echinoderms, the endoskeleton consists of calcareous ossicles embedded in the dermis.

Structure and organization: The vertebrate endoskeleton is divided into axial (skull, vertebral column, rib cage) and appendicular (limbs and girdles) components. Bone is a dynamic, living tissue capable of growth, remodeling, and repair. Cartilage provides flexible support in joints and in the developing skeleton. Bone marrow within certain bones produces blood cells.

Development and evolution: In vertebrates, most bones originate from cartilage templates (endochondral ossification) or directly from mesenchyme (intramembranous ossification). The skeleton grows in size and density through remodeling by osteoblasts and osteoclasts. Evolutionarily, endoskeletons allow greater body size and mobility than exoskeletons.

Function: The endoskeleton provides structural support, protects vital organs, enables movement via lever systems with muscles, and serves as a mineral reservoir (calcium and phosphate). In many vertebrates, hematopoietic tissue in bone marrow also contributes to blood cell formation.

Variations and examples: Vertebrates show a wide range of endoskeletal structures from the lightweight skeletons of birds to the dense bones of mammals. Cartilaginous fishes have primarily cartilaginous skeletons; most other fishes show ossified endoskeletons. Echinoderms possess an internal skeleton of ossicles.

Clinical relevance: In medicine, skeletal health affects mobility and function; conditions include osteoporosis, fractures, arthritis, and congenital skeletal disorders. Treatment may involve nutrition, physical therapy, or surgical implants.